Enable ppc64le builds for Travis-CI
Enable ppc64le builds for Travis-CI

This also disables AMD64 builds for now.

Based on https://github.com/gridcf/gct/pull/137 by Eshant Gupta.

gridcf/gct,gridcf/gct,gridcf/gct,gridcf/gct,gridcf/gct,gridcf/gct